Manufacture of patent leather



Patented Apr. 10, 1934 UNITED STATES 1,954,150 MANUFACTURE or PATENT LEATHER Home 11. Hopkins, Bidley Park, Pa, assignor to E. I. du Pont de Nemours a Company, Wilmington, DeL, a corporation of Delaware No Drawing.-

IClaims.

This invention relates tothe manufacture of patent leather and moreparticularly to an improved outer or top coating for patent leather finishes. m

One of the chief disadvantagesinthe manufacture of patent leather resides in the long sunning treatment required to dry and remove the tack after completion of the process. While diiferent manufacturers carry out the process according to their own unique procedure, which may involve trade secrets, the following two methods may be considered essentially typical of the methods commonly used; all of which methods necessitate the expensive sunning treatment referred to.

One widely used method of manufacturing patent leather is substantially as follows:

A heavy consistency first coat of a mixture of japanners oil (bodied linseed oil) and a pig- 2o ment is applied to the leather and rubbed in with the hands. Two or three coats of clear varnish, consisting of iapanners oil thinned with naphtha, are next applied. These coats of clear varnish, as well asthe first mentioned coating of pigmented japanners oil, are applied with a sponge and are dried overnight at about 90-l00 F. A final coat of japannersvarnish (strongly boiled linseed oil) is now flowed on, and the leather baked in a japanners oven for about sixteen hours at approximately 160 F. To remove the final tack from the top coat varnish it must be exposed to sunlight for at least five hours, the only possible alternative for sunning being the very expensive ultraviolet irradiating equipment which is rarely used in this country. In spite of the sunning the finish is often still tacky or sticky at slightly elevated temperatures and is often waxed or packed in waxed paper to prevent sticking during shipp s.

A second method, sometimes used in the manuiacture of patent leather, is to apply a finish in which pyroxylin is utilized. The pyroxylin finish, doesnot require quite as much sunning, and dries slightly better, but it is considerably more expensive than the oil type finish. In this case the entire finish consists of a mixture of pyroxylin and japanners oil, thinned to a suitable consistencyior applying with a blunt edged metal kniie. Four or five coats of this mixture are epplied, each being dried overnight at about 90 F.

Application December 18, 1930, Serial No. 503,227

ess that depends on the'weather as completely as does this one, is subject to many uncertainties. There are times, especially during the winter months,- when production may be held up for weeks due to the absence of sun which is necessary for the final operation. In the winter, when the weather is liable to be most cloudy, the leather needs a longer time of sunning due to the smalleramount of ultraviolet light in the sun's rays at that season. In addition to the difliculties in-- volved in the manufacturing process, a second disadvantage resides in the defects inherent in the product itself. In this connection may be mentioned the fact that these finishes are subject.

to rapid embrittling which produces large unsightly cracks in the patent leather product.

This invention has as an object a method of manufacturing patent leather which does not require sunning or exposure to ultraviolet light. Another object is the production of patent leather having a top coat finish which gives a more permanent retention of flexibility, and hence elimination of the earily'cracking' of the finish, so common in previously known types of patent leather.

These objects are accomplished by. the follow ing invention in which a varnish comprising a solution ci. a synthetic resin 01 the polyhydric alcohol-polybasic acid type, modified with a drying oil, with or without small proportions cc! other ingredients, is applied as a top coat in the manufacture of patent leather.

In accordance with the practice of the present invention the final coat of oil vamish'applied in the processes referred to above, is omitted and in lieu thereof is applied a top coat of a solution of a drying oil modified polyhydrlc alcohol-polybasic acid resin. This coating may be a solution in any suitable solvent'ior the particular resin or resins used, and may contain small quantities of additional ingredients, which in some way enhance the value of the coating.

Polyhydric alcohol-polybasic acid resins modified in any desired proportions with drying oils may be used, but resins of the following compositions, expressed in terms of the reacting constituents, have been found to be especially suitable:

Resin A Parts by weight Glycerol 12.6 Phthalic anhydride 29.7 Linseed oil 57.7

Resz'nB Parts by weight Glycerol 12.60 Phthalicanhydride 29.70 Linseed oil 28.85 Chinawood oil 28.85

The glyceryl phthalate in the preceding two resins constitutes about 40% by weight of the resin.

Resin 0 Parts by weight Glycerol 10.8 Phthalic anhydride 26.2 Perilla oil 63.0

This resin contains about 35% by weight of glyceryl phthalate.

- ResinD Parts by weight Glycerol 14.1 Phthalic anhydride 33.3 Soya bean oil 52.6

This resin contains about 45% by weight of glyceryl phthalate.

The foregoing resins may be made by any of the methods commonly used for the manufacture of oil modified polyhydric alcohol-polybasic acid resins. As indicated in the examples the preferred polyhydric alcohol is glycerol and the preferred polybasic acid is phthalic anhydride. Other polyhydric alcohols and-bolybasic acids, known by those skilled in the art of manufacturing this type of resin, may be used. Among the polyhydric alcohols commonly used are pentaerythritol, polyethylene glycol, etc. Examples of other suitable polybasic acids are, succinic acid, fumaric acid, maleic acid, and adipic acid.

Instead of drying oils, the equivalent amount of drying oil acids may be used in manufacturing these resins as understood by those skilled in the art. The drying oil mentioned in the claims refers, therefore, to the drying oil acids as well as to the drying oil itself. Additional ingredients which may be incorporated with the resins in small amounts (for example, up to.10%) are rosin or other resin acids, mixtures of monohydric (e. g. benzyl) or polyhydric alcohols (e. g. ethylene glycol) as well as substituted polyhydric alcohols such as glycol ethers. Certain high boiling organic substances such as xylol, solvent naphtha,

terpenes, turpentine substitutes, and many others may be incorporated. If desired certain metallic driers, such as cobalt, lead, manganese, or iron linoleate may be used to speed up the drying of the finish.

The coating may be applied to the flexible base material by brushing, spraying, swabbing, or by any suitable method, preferably at such a consistency that the solution as applied contains about 40-60% of solid material. The leather is then baked in order to suitably dry the film, about 10 to 20 hours at about 150 to 175 F. having been found suitable.

This invention has several important advantages over the production of patent leather by the methods heretofore used. One of these advantages relates to the manufacture of the patent leather and resides in the fact that no sunning is necessary because the hardening, in the present case, is accomplished by baking. This is possible with my new finish because, while the previously used oil films set up almost entirely by oxidation, the resin films of the present invention harden by a combination of oxidation and polymerization, the latter process being appreciably hastened by heat.

Because of the exceptional toughness and lasting flexibility of the film yielded by the particular type of resin used, the new finish retains its flexibility for a considerably longer period than the old type of finish, and thus remains free from cracks for a longer period of time.

A further advantage resides in the fact that my new patent leather is almost entirely free from the residual tackiness which is often present in patent leather even after sufficient sunning. This feature is especially important if the leather is to be packed for shipment through any great distance, and especially if it is to be subjected to elevated temperatures, as in shipping through warm regions. An entire shipment of excellent quality patent leather is sometimes lost because the packed sheets have stuck together, and cannot be separated without tearing great holes in the coating.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process of manufacturing patent leather which comprises subjecting leather to treatment with a composition comprised of japanners oil, applying over the coating or coatings applied in such treatment a coating comprising a drying oil modified polyhydric alcohol-polybasic acid resin, and baking to harden the resin coating.

2. A process of manufacturing patent leather which comprises subjecting leather to treatment with a composition comprising J'apanners oil, applying over the coating or coatings applied in such treatment a coating comprised of the resinous reaction product of glycerol, phthalic anhydride, and a drying oil.

3. A step in a process for manufacturing patent leather which comprises applying acoating of a drying oil modified glyceryl phthalate resin containing in combined formfrom about 52% to 63% drying oil over the previously applied undercoats, and baking the product.

4. In the manufacture of patent leather products the steps of applying a pyroxylin-oil undercoat and pplyinz a top coat of oil modified polyhydric lcohoI-polybasic acid resin.

5. In the manufacture of patent leather prodacts the steps of applying a. pyroxyiin-containing u'ndercoat and applying a. top coat of oil modified polyhydric alcohol-polybasic acid resin.

6. A patent leather product having an undercoat comprising a dried film of pyroxylin-oil HORACE H. HOPKINS. 

